This application claims priority of Korean Application No. 2001-52600, filed on Aug. 29, 2001 in the Korean Patent Office, the entire content of which is incorporated herein by reference.
The present invention relates to a vacuum fluorescent display, and more particularly, to a vacuum fluorescent display which has a rib grid.
Generally, a vacuum fluorescent display (VFD) is a light-emitting display device wherein thermal electrons emitted from cathode filaments selectively land on a phosphor layer by way of a control electrode and an anode electrode to thereby produce light. Since a VFD has excellent visibility, a wide viewing angle, a low driving voltage, and high reliability, it is well adapted for use as a display device in various fields.
In a VFD, a metallic mesh-type grid (referred to hereinafter simply as the xe2x80x9cmesh gridxe2x80x9d) is used as the control electrode.
The mesh grid is formed with a mesh that is produced through etching a thin metal plate of stainless steel (SUS). The mesh grid is mounted on a substrate with a phosphor layer while being supported by a support at its periphery such that it is spaced apart from the substrate at a predetermined distance.
In order to make the thermal electrons land on the intended point of the phosphor layer and prevent the electrons from hitting unintended points on the phosphor layer, there should be a predetermined distance between the support and the anode electrode as well as between the mesh grid and the substrate. However, in such a case, it becomes difficult to pattern the VFD with a mesh grid such that it is provided with a minute pattern or a complex polygonal pattern.
Furthermore, the mesh grid is liable to sink at its center due to thermal deformation in use or during the fabrication process. In this case, the capacity of the mesh grid for accelerating and diffusing the thermal electrons becomes deteriorated in such a way that a brightness difference between the neighboring phosphor occures.
In order to prevent the mesh grid from sinking at its center, the mesh grid may be mounted on the substrate while being supported by a plurality of supports. However, as the number of the supports is increased, the pattern design for the anode electrode becomes more limited.
In order to solve such a problem, Japanese Patent Publication No. Hei 6-251732 discloses a grid for a VFD, with the following features, as shown in FIG. 5. A carbon layer 112 and a phosphor layer 114 are formed at the substrate in a predetermined pattern, and an insulating rib 116 is mounted around the carbon layer 112 and the phosphor layer 114. A conductive material layer 118 is formed at the top surface of the rib 116 while bearing the same pattern as the rib 116.
The insulating rib 116 rises above the phosphor layer 114 by 20xcexcm or more to prevent a short circuit between the conductive material layer 118 and the phosphor layer 114. That is, the insulating rib 116 and the conductive material layer 118 are disposed around the phosphor layer 114 while being used as a grid.
As the insulating rib 116 rises above the phosphor layer 114, when the thermal electrons reach the phosphor layer 114, some of the thermal electrons are liable to be accumulated at the surface of the insulating layer 119 around the insulating rib 116, and remain charged.
In this case, the electric fields distributed at the phosphor layer 114 are non-uniformly formed under the influence of the charged electrons so that light emission spots occur at the phosphor layer 114.
In order to solve such a problem, Japanese Patent Publication No. Hei 8-138591 discloses a VFD with the features as shown in FIG. 6. A conductive layer 122 and a phosphor layer 124 are formed at the substrate 120, and an insulating rib 126 is formed on the conductive layer 122 around the phosphor layer 124 while rising above the phosphor layer 124. A grid electrode 128 is formed at the top surface of the insulating rib 126, and a subsidiary insulating rib 126xe2x80x2 and a subsidiary grid electrode 128xe2x80x2 are formed on the insulating layer 129 around the conductive layer 122 while bearing the same pattern as the insulating rib 126 and the grid electrode 128.
The conductive layer 122 prohibits accumulation of electrons at the surface of the insulating layer 129, thereby preventing occurrence of light emission spots at the phosphor layer 124.
However, the above technique results in the following problem. In order to form the insulating rib, an insulating paste is printed at a predetermined thickness (for instance, 10-30 xcexcm), and dried. This process is repeated three to fifteen times. Furthermore, the formation of the grid electrode on the insulating rib should be done in the same manner. Therefore, much time is consumed for the repeated printings, and the production efficiency deteriorates.
When the grid electrode is formed through printing a conductive material, gas generated from the conductive material may remain within the vacuum tube. In this case, the flowing of the thermal electrons to the phosphor layer is obstructed by the remaining gas, and the gas is attached to the filaments or the phosphor layer and prohibits the fluent operation of the display device. Therefore, the brightness or the life span of the display device deteriorates.
In the case the occurrence of light emission spots at the phosphor layer is prevented by way of the subsidiary insulating rib and the subsidiary grid electrode, the pattern design for the VFD is limited due to the additional components.
In one embodiment, the present invention provides a vacuum fluorescent display VDF that secures a pattern formation space in an easy manner while preventing occurrence of light emission spots at the phosphor layer.
In one embodiment, the present invention provides a VDF that prevents deterioration in the brightness and the life span of the VDF due to the impurities occurring during the processing in one embodiment.
In one embodiment, the VDF includes a vacuum tube with a pair of substrates, and a side glass disposed between the two substrates. Filaments are mounted within the vacuum tube to emit thermal electrons. A conductive layer is formed at one of the substrates with a predetermined pattern, and a phosphor layer is formed on the conductive layer. A rib grid is provided at the substrate with an insulating rib positioned around the conductive layer, and a control electrode is formed on the top surface of the insulating rib. Assuming that the distance between the top surface of the substrate and the top surface of the insulating rib is indicated by h1 and the distance between the top surface of the substrate and the top surface of the phosphor layer is indicated by h2, it is established that h1xe2x89xa6h2.
In one embodiment, the control electrode is formed with a metallic material while bearing a single-layered structure. The metallic material for the control electrode is selected from stainless steel, platinum, silver, or copper.
The insulating rib rises above the conductive layer, and the control electrode rises above the phosphor layer.
An extension may be extended from the top end of the control electrode toward the center of the phosphor layer, in one embodiment.
In one aspect, the invention describes a vacuum fluorescent display comprising: a vacuum tube with a pair of substrates, and a side glass disposed between the two substrates; filaments mounted within the vacuum tube to emit thermal electrons; a conductive layer formed at one of the substrates with a predetermined pattern; a phosphor layer formed on the conductive layer; and a rib grid having an insulating rib positioned around the conductive layer, and a control electrode formed on the top surface of the insulating rib; wherein when the distance between the top surface of one of the substrates and the top surface of the insulating rib is indicated by h1 and the distance between the top surface of the substrate and the top surface of the phosphor layer is indicated by h2, it is established that h1xe2x89xa6h2.